diff --git a/category-syncer.js b/category-syncer.js
index dea5241..55bc0cb 100644
--- a/category-syncer.js
+++ b/category-syncer.js
@@ -61,12 +61,11 @@ class CategorySyncer extends EventEmitter {
         try {
             await this._syncFromDb();
             const duration = Date.now() - startTime;
-            console.log(`✅ Sync completed successfully in ${duration}ms.`);
 
-            // Log next sync time
+            // Log completion and next sync time
             const syncInterval = parseInt(process.env.SYNC_INTERVAL_MS) || 60000;
             const minutes = Math.round(syncInterval / 60000);
-            console.log(`⏰ Next sync in ${minutes} minute${minutes !== 1 ? 's' : ''}`);
+            console.log(`✅ Sync completed in ${duration}ms. Next sync in ${minutes} minute${minutes !== 1 ? 's' : ''}`);
         } catch (err) {
             console.error('❌ Sync failed:', err);
         } finally {
diff --git a/index.js b/index.js
index f4a4926..ff6c9d1 100644
--- a/index.js
+++ b/index.js
@@ -43,4 +43,4 @@ process.on('SIGINT', () => {
 });
 
 // Start Express server
-startServer();
+startServer(categorySyncer);
diff --git a/picture-syncer.js b/picture-syncer.js
index 74a2bd0..3c8ebd5 100644
--- a/picture-syncer.js
+++ b/picture-syncer.js
@@ -9,10 +9,48 @@ class PictureSyncer {
             return PictureSyncer.instance;
         }
         this.cacheBaseDir = process.env.CACHE_LOCATION || '.';
+
+        // Track syncing state per group
+        this.isSyncing = new Map(); // groupName -> boolean
+        this.queuedSyncs = new Map(); // groupName -> { imageIds, groupName }
+
         PictureSyncer.instance = this;
     }
 
     async syncImages(imageIds, groupName) {
+        // Check if already syncing this group
+        if (this.isSyncing.get(groupName)) {
+            if (this.queuedSyncs.has(groupName)) {
+                console.log(`🚫 Image sync for '${groupName}' already in progress and queued. Ignoring.`);
+                return;
+            }
+            console.log(`⏳ Image sync for '${groupName}' already in progress. Queuing.`);
+            this.queuedSyncs.set(groupName, { imageIds, groupName });
+            return;
+        }
+
+        await this._doSync(imageIds, groupName);
+    }
+
+    async _doSync(imageIds, groupName) {
+        this.isSyncing.set(groupName, true);
+
+        try {
+            await this._performSync(imageIds, groupName);
+        } finally {
+            this.isSyncing.set(groupName, false);
+
+            // Process queued sync for this group if any
+            if (this.queuedSyncs.has(groupName)) {
+                console.log(`🔄 Processing queued image sync for '${groupName}'...`);
+                const queued = this.queuedSyncs.get(groupName);
+                this.queuedSyncs.delete(groupName);
+                setImmediate(() => this.syncImages(queued.imageIds, queued.groupName));
+            }
+        }
+    }
+
+    async _performSync(imageIds, groupName) {
         const groupDir = path.join(this.cacheBaseDir, 'img', groupName);
 
         // Ensure directory exists
@@ -74,8 +112,12 @@ class PictureSyncer {
                 for (const record of result.recordset) {
                     if (record.bBild) {
                         const filePath = path.join(dir, `${record.kBild}.avif`);
-                        // Convert to AVIF using sharp
+                        // Resize to 130x130 and convert to AVIF using sharp
                         await sharp(record.bBild)
+                            .resize(130, 130, {
+                                fit: 'cover',
+                                position: 'center'
+                            })
                             .avif({ quality: 80 })
                             .toFile(filePath);
                     }
diff --git a/server.js b/server.js
index 6147a30..9f03181 100644
--- a/server.js
+++ b/server.js
@@ -6,27 +6,86 @@ import fs from 'fs/promises';
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = path.dirname(__filename);
 
-export function startServer() {
+export function startServer(categorySyncer) {
     const app = express();
     const PORT = process.env.SERVER_PORT || 3000;
     const HOST = process.env.SERVER_HOST || '0.0.0.0';
     const CACHE_DIR = process.env.CACHE_LOCATION || './cache';
 
-    // Serve category tree JSON
-    app.get('/api/categories', async (req, res) => {
+    // Cache for ETags and data
+    const cache = {
+        categories: { etag: null, data: null },
+        html: { etag: null, data: null }
+    };
+
+    // Function to calculate ETag for categories
+    async function updateCategoriesCache() {
         try {
             const treePath = path.join(CACHE_DIR, 'category_tree.json');
             const data = await fs.readFile(treePath, 'utf-8');
-            res.json(JSON.parse(data));
+            const crypto = await import('crypto');
+            cache.categories.etag = crypto.createHash('md5').update(data).digest('hex');
+            cache.categories.data = data;
+        } catch (err) {
+            // Silently skip if file doesn't exist yet (will be created on first sync)
+            if (err.code !== 'ENOENT') {
+                console.error('Error updating categories cache:', err);
+            }
+        }
+    }
+
+    // Function to calculate ETag for HTML
+    async function updateHtmlCache() {
+        try {
+            const htmlPath = path.join(__dirname, 'index.html');
+            const data = await fs.readFile(htmlPath, 'utf-8');
+            const crypto = await import('crypto');
+            cache.html.etag = crypto.createHash('md5').update(data).digest('hex');
+            cache.html.data = data;
+        } catch (err) {
+            console.error('Error updating HTML cache:', err);
+        }
+    }
+
+    // Initialize caches on startup
+    updateHtmlCache();
+    updateCategoriesCache();
+
+    // Update categories cache when sync completes
+    if (categorySyncer) {
+        categorySyncer.on('synced', ({ changed }) => {
+            if (changed) {
+                updateCategoriesCache();
+            }
+        });
+    }
+
+    // Serve category tree JSON (with ETag for conditional caching)
+    app.get('/api/categories', async (req, res) => {
+        try {
+            // Check if client has cached version
+            if (req.headers['if-none-match'] === cache.categories.etag) {
+                return res.status(304).end(); // Not Modified
+            }
+
+            // Set cache headers with ETag
+            res.set('Cache-Control', 'public, max-age=60, must-revalidate');
+            res.set('ETag', cache.categories.etag);
+
+            res.json(JSON.parse(cache.categories.data));
         } catch (err) {
             res.status(500).json({ error: 'Failed to load category tree' });
         }
     });
 
-    // Serve category images
+    // Serve category images (long cache - images rarely change)
     app.get('/img/cat/:id.avif', (req, res) => {
         const { id } = req.params;
         const imagePath = path.join(CACHE_DIR, 'img', 'categories', `${id}.avif`);
+
+        // Cache images for 1 year (immutable content)
+        res.set('Cache-Control', 'public, max-age=31536000, immutable');
+
         res.sendFile(path.resolve(imagePath), (err) => {
             if (err) {
                 res.status(404).send('Image not found');
@@ -34,16 +93,24 @@ export function startServer() {
         });
     });
 
-    // Serve index.html
-    app.get('/', (req, res) => {
-        const htmlPath = path.join(__dirname, 'index.html');
-        console.log('Attempting to serve:', htmlPath);
-        res.sendFile(htmlPath, (err) => {
-            if (err) {
-                console.error('Error serving index.html:', err);
-                res.status(500).send('Error loading page');
+    // Serve index.html (with ETag for conditional caching)
+    app.get('/', async (req, res) => {
+        try {
+            // Check if client has cached version
+            if (req.headers['if-none-match'] === cache.html.etag) {
+                return res.status(304).end(); // Not Modified
             }
-        });
+
+            // Set cache headers with ETag
+            res.set('Cache-Control', 'public, max-age=300, must-revalidate');
+            res.set('ETag', cache.html.etag);
+            res.set('Content-Type', 'text/html');
+
+            res.send(cache.html.data);
+        } catch (err) {
+            console.error('Error serving index.html:', err);
+            res.status(500).send('Error loading page');
+        }
     });
 
     app.listen(PORT, HOST, () => {